Pandemic flu vaccine protected pregnant women

NEW YORK (Reuters Health) - The vaccine against the new 2009 flu strain offered high levels of protection for pregnant women and their babies, a new study from France suggests.

Three weeks after the expectant mothers got the vaccine against the novel H1N1 flu, 98 percent of them had developed protective levels of antibodies against the virus, researchers found.

And when their babies were born, 95 percent of them had enough antibodies to be considered protected as well, report Dr. Vassilis Tsatsaris from Groupe Hospitalier Cochin-Saint Vincent de Paul in Paris and colleagues.

"Vaccination during pregnancy protects infants during the first months of life, when vaccination cannot be performed," the researchers write in their report, published in the Annals of Internal Medicine.

In the U.S., health officials and physician organizations urge pregnant women to get the seasonal flu vaccine, which now contains the new H1N1 strain that emerged in 2009.

This is especially important because expectant mothers are at higher risk of getting severely ill from the flu, presumably due to changes in the immune system caused by the pregnancy.

In the new work, the French researchers followed 107 healthy pregnant women who had received a single shot against the 2009 virus during the second or third trimester.

The study wasn't large enough to test protection in terms of actual flu cases, and it didn't include a comparison group of unvaccinated women.

Instead, the researchers measured antibodies against the virus in blood drawn from the women and from the umbilical cord of their babies. Then they determined how many developed enough antibodies to protect them against the flu 70 percent of the time.

Three weeks following the shot, 98 percent of the women were protected -- up from 19 percent before. By the time they gave birth, that number had dropped only slightly -- to 92 percent -- and most babies also had high levels of antibodies.

According to the researchers, theirs is the first study to look at the immune response of expectant mothers and their babies after a flu shot against the novel H1N1 strain.

The work was supported by the French National Institute of Health and Medical Research. Vaccine maker Sanofi Pasteur provided the vaccines and also analyzed the blood samples.

While there were no confirmed cases of flu, there were several medical problems among the women and babies in the study. According to an independent expert committee, however, none of them was caused by the vaccine.

The researchers did not respond to requests for comments.

In June, a U.S. government study found the number of health problems among pregnant women who received the pandemic flu shot was no different from what would be expected in the general population. (See Reuters Health story of June 29, 2011.)

"No reasons exist from this report not to continue to follow the (Centers for Disease Control and Prevention) recommendations and, pending more information, consider that the benefits of influenza immunizations in pregnant women outweigh the risks," Dr. Michael Schatz of Kaiser Permanente Medical Center told Reuters Health at the time.

While some flu vaccines contain the mercury-based preservative thimerosal, a study out last year found the compound did not increase the risk of autism, as some have worried. (See Reuters Health story of September 13, 2010.)

For those who still worry, thimerosal-free alternatives are available.